Some time ago, I made the clame that the SP10 was a good choice of DD turntable because it contained no special IC's, so was repairable. Well, due to my own ineptness last weekend I have been forced to see how true that was. Saturday morning, the turntable looked ill, it was buzzing to itself, the strobe was flashing in it sown time and the motor was trying to go in both directions at once. So I first checked the power supply, and that seemed ok, though there were 2mv burst of RF at 100hz intervals. So next the table was removed from he slate, and the bottom taken off. Nothing obvious. The I realised that there was nothing in the turntable that knew about the 50hz frequency that the thing was humming at. So measuring the power lines again under load, I found that the 5v line was dropping out at 50hz, so I was in luck the problem seemed to be the supply. After dismantling that I noticed a cap was leaking electrolyte, and it was in just the place to cause the problem. So replacing that fixed the 5v rail problem, and wonders the table worked again. So before putting the bottom back on I decided to measure the supply rails in the table. And they were fine. Until the probe slipped and shorted the 32.5v motor supply to the 5v logic supply. At which point all the TTL logic on the control board died
So I have just spent the last two nights soldering and replacing 16 14pin DIP logic chips, and replacing with thier modern 74LS equivalents. And wonders of wonders it works again. Ok, there is still a small problem in the start stop debounce isn't working verru well, so stopping the thing can be a problem, but hopefully I can fix thet without breaking anything else.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
Blummen lubricated meter probes!
